Page 262 in
The Book:
"It has also been suggested by Pollack and Dodds that the wrappig can be carried out in a hexagonal configuration.
Sn,m = (n^2 + m^2 + nm) modulo N"
which is the same as the normal square 2D except for the added "nm" inside the parenthesis. Note that this is not the same 2D sequence as normal square 2D QRD's. The hex stacking would make the round hole packing lots more effective!